Potassium Channel Blocker (Neuromuscular Junction Facilitator) Pregnancy: Should not be used during pregnancy; women of childbearing potential must use effective contraception during treatment. No adequate clinical data on exposed pregnancies; in rats an increase in the number of mothers delivering still-born offspring was observed. Breastfeeding: it is not known whether amifampridine is excreted in human breast milk (it is present in animal milk) — decide whether to discontinue breastfeeding or therapy, taking account of the benefit of each.

Amifampridine

Brand names: Firdapse, Zenas

A potassium channel blocker used to treat the symptoms of Lambert-Eaton myasthenic syndrome in adults.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Starting dose 15 mg daily in divided doses, increased in 5 mg increments every 4 to 5 days

Route: Oral (tablets taken with food)

Frequency: In divided doses, three or four times a day

Max: 60 mg per day; no single dose should exceed 20 mg

Treatment should be initiated under the supervision of a physician experienced in the treatment of the disease (Lambert-Eaton myasthenic syndrome). Tablets are to be taken with food. If treatment is discontinued, patients may experience some of the symptoms of LEMS. Clinical and ECG monitoring are indicated at the start of treatment and yearly thereafter; if signs or symptoms of cardiac arrhythmia occur, perform an ECG immediately. Seizure risk is dose-dependent — discontinue treatment in the event of a seizure. Paediatric population: safety and efficacy in children aged 0 to 17 years has not been established and no data are available (UK SPC). NOTE FOR REVIEWER: this UK SPC caps the dose at 60 mg/day, which is lower than the 80 mg/day maximum currently shown on the page — the page figure is not supported by this source. The US label (FIRDAPSE, Catalyst) differs and should not be merged in: it gives 15 mg to 30 mg daily in 3 to 5 divided doses for adults and children weighing 45 kg or more, increasing by 5 mg every 3 to 4 days, maximum single dose 20 mg and maximum 100 mg daily; and for paediatric patients weighing under 45 kg (from 6 years) 5 mg to 15 mg daily in 3 to 5 divided doses, increasing by 2.5 mg every 3 to 4 days, maximum single dose 10 mg and maximum 50 mg daily.

Dose adjustments

Renal

Use with caution in renal or hepatic impairment and monitor carefully. Moderate or severe renal or hepatic impairment: starting dose 5 mg (half a tablet) once daily. Mild renal or hepatic impairment: starting dose 10 mg daily (5 mg twice a day). Titrate more slowly than in patients without impairment, in 5 mg increments every 7 days, and stop upward titration if any adverse reaction occurs.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Epilepsy
Uncontrolled asthma
Concomitant use with sultopride
Concomitant use with medicinal products with a narrow therapeutic window
Concomitant use with medicinal products with a known potential to cause QTc prolongation
Patients with congenital QT syndromes

Side effects

Paraesthesias, including peripheral and peribucal paraesthesia, oral paraesthesia and oral hypoaesthesia (very common) — the most commonly reported reaction
Nausea (very common); abdominal pain (common); diarrhoea and epigastralgia (frequency not known)
Dizziness and hypoaesthesia (very common); convulsions, chorea, myoclonia, drowsiness, weakness, fatigue and headache (frequency not known)
Hyperhidrosis and cold sweat (very common); cold extremities (common); Raynaud's syndrome (frequency not known)
Cardiac rhythm disorders and palpitations (frequency not known)
Bronchial hypersecretion, cough, and asthma attack in asthmatic patients or those with a history of asthma; elevated liver enzymes (transaminases); sleep disorders and anxiety; blurred vision (all frequency not known)

Interactions

Sultopride — concomitant use contraindicated
Medicinal products with a known potential to cause QTc prolongation — concomitant use contraindicated
Medicinal products with a narrow therapeutic window — concomitant use contraindicated; there are no data on the effects of amifampridine on the metabolism or active secretion of other medicinal products, so special care is needed with concomitant treatments eliminated by metabolism or active secretion
Medicinal products known to lower the epileptic threshold — increase the dose-dependent risk of seizures (§4.4)
The §4.5 text is truncated in this source extract, so the interaction list is incomplete. US labelling additionally flags drugs with cholinergic effects (e.g. direct or indirect cholinesterase inhibitors), which may increase cholinergic effects and adverse reactions

Clinical monograph

How it works

It blocks presynaptic voltage-gated potassium channels, prolonging nerve terminal depolarisation and enhancing calcium-dependent acetylcholine release at the neuromuscular junction.

Prescribing in practice

It can lower the seizure threshold and is contraindicated in epilepsy, and it may prolong the QT interval so caution is needed with other QT-prolonging drugs.
It should be initiated and supervised by a specialist experienced in managing Lambert-Eaton myasthenic syndrome.
Because the syndrome is frequently paraneoplastic, an underlying malignancy (particularly small-cell lung cancer) should be excluded and monitored for.

Monitoring

Monitor clinically for seizures and consider electrocardiographic assessment where there are additional risk factors for QT prolongation.

Counselling the patient

Report any fits, twitching, or unusual heart sensations promptly.
Do not stop the medicine suddenly without specialist advice as symptoms may return.
Attend follow-up for ongoing screening related to the underlying condition.

Evidence & guidelines

Use is supported by its licensed indication for Lambert-Eaton myasthenic syndrome and specialist neuromuscular guidance.

Reference: NICE TA605 (Amifampridine for Lambert-Eaton myasthenic syndrome, 2020); Orphanet / European Neuromuscular Centre guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways